1. Field of the Invention
This invention is related to a method of forming cylindrical bumps on a substrate for integrated circuits, which comprises the step of covering the substrate with a screening material, forming openings in the screening material to align with the copper circuits of the substrate, filling the openings with pure copper or high melting point metal to form cylindrical bumps, and then forming a layer of solder alloy on the top of each of the cylindrical bumps.
2. Description of the Prior Art
In the conventional flip chip technological process for connecting a die 2xe2x80x2 to a substrate 1xe2x80x2 (see FIGS. 1a and 1b), it is necessary to form under-bump-metallurgy (UBM) layers 21xe2x80x2 from the input/output (I/O) of the die 2xe2x80x2 and bumps 22xe2x80x2 of solder alloy on the under-bump-metallurgy layers 21xe2x80x2, and then turn over the die 2xe2x80x2 to engage the substrate 1xe2x80x2 (copper circuits 12xe2x80x2 have already been formed on the board 11xe2x80x2 of the substrate 1xe2x80x2). Thereafter, a underfill 3xe2x80x2 is filled between the substrate 1xe2x80x2 and the die 2xe2x80x2.
However, the bumps 22xe2x80x2 made of solder alloy will be melted in a process at 100xcx9c350 degrees centigrade so that the gravitational force will lower the position of the die 2xe2x80x2 thus reducing the distance between the bumps 22xe2x80x2 of the die 2xe2x80x2 and the substrate 1 and therefore increasing the difficulty in filling the underfill 3xe2x80x2. Hence, this method always results in some cylindrical bumps being defective, the numbers of which cannot be reduced.
Therefore, it is an object of the present invention to provide a method of forming cylindrical bumps on a substrate for integrated circuits which can obviate and mitigate the above-mentioned drawbacks.
This invention is related to a method of forming cylindrical bumps on a substrate for integrated circuits, which comprises the step of covering the substrate with a screening material, forming openings in the screening material to align with the copper circuits of the substrate, filling the openings with pure copper or high melting point metal to form cylindrical bumps, and then forming a layer of solder alloy on the top of each of the cylindrical bumps.
It is the primary object of the present invention to provide a method of forming bumps on a substrate for integrated circuits which includes the steps of increasing the thickness of the copper circuits and then electroplating a layer of solder alloy on the copper circuits so that the solder alloy will be melted but the copper or high melting point metal will not be melted in operation at temperatures between 100xcx9c350 degrees cenfigrade, thereby enabling the distance between the die and the substrate to be accurately controlled and therefore facilitating the filling of underfill.
It is another object of the present invention to provide a method of forming cylindrical bumps on a substrate for integrated circuits wherein the bumps are formed on the substrate instead of the die so that even if there is something wrong with the process of forming bumps on the substrate, the die has no need to be discarded, thereby decreasing the manufacturing cost.
It is a further object of the present invention to provide a method of forming cylindrical bumps on a substrate for integrated circuits which only requires the die to be coated with a under-bump-metallurgy layer rather than a under-bump-metallurgy layer and formation of bumps on the under-bump metallurgy layer as required by the conventional method, thereby reducing the time and cost of manufacturing dies.
The foregoing objects and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example.